In general, in rotary machines such as turbines and centrifugal compressors, a sealing mechanism is provided to prevent a fluid from leaking from a gap between a stationary side and a rotating side.
Such a sealing mechanism is generally a non-contact sealing mechanism from the viewpoint of, for instance, a maintenance characteristic. However, the non-contact sealing mechanism needs to set as small a clearance as possible in order to reduce the leakage of a fluid.
The sealing mechanism may give rise to self-excited vibration due to a swirl flow (hereinafter referred to simply as “swirl”) of an entering fluid. In the sealing mechanism, the clearance should be set to prevent the stationary side and the rotating side from being brought into contact by such self-excited vibration. For this reason, in the non-contact sealing mechanism, it is impossible to reduce the clearance, and it is difficult to further reduce the leakage of the fluid.
There is a proposal for a technique that counteracts the swirl responsible for the self-excited vibration by ejecting a high-pressure fluid with respect to the fluid flowing into a gap between the stationary side and the rotating side (for example, see Patent Literatures 1 and 2).
On the other hand, as the non-contact sealing mechanism capable of reducing the swirl, a so-called hole seal having innumerable holes formed in an inner circumferential surface of the stationary side is known. When such a hole seal is used, a vortex is generated in the holes. The vortex in the holes interferes with the swirl, and the swirl is suppressed.